Processes for retorting oil shale

ABSTRACT

An improvement in the processes for the recovery of volatile material from solid carbonaceous material, such as oil shale, tar sands, coal, lignite, and the like, which comprises controlling the atmosphere surrounding the carbonaceous material during retorting. The atmosphere is controlled to contain natural gas or a gas of similar composition or mixtures of natural gas and up to 20 percent carbon dioxide. Improved yields are achieved in various retorting processes.

United States Patent inventors Appl. No. Filed Patented Assignee PROCESSES FOR RETORTING 01L SHALE 7 Claims, 2 Drawing Figs.

U.S. Cl 208/11,

201/29, 201/32, 201/36 Int. Cl Cl0g 1/02 Field of Search 201/29, 31,

Primary Examiner-Curtis R. Davis Attorney-McLean, Morton & Boustead ABSTRACT: An improvement in the processes for the recovery of volatile material from solid carbonaceous materia1, such as oil shale, tar sands, coal, lignite, and the like, which comprises controlling the atmosphere surrounding the carbonaceous material during retorting. The atmosphere is controlled to contain natural gas or a gas ofsimilar composition or mixtures of natural gas and up to 20 percent carbon dioxide. Improved yields are achieved in various retorting processes.

PROCESSES FOR RETORTING OIL SHALE This invention relates to an improvement in the processes of removing volatile material, such as combustible gasses, liquid motor fuels, and various grades of oil from solid carbonaceous material such as oil shale, tar sand, coal, lignite and the like.

Many techniques have been employed for the benefication of solid carbonaceous material. For example, oil shale has been retorted in batch-type fixed bed operations, rotating drums, chain grate kilns, moving bed retorts and fluidized beds. These basic types of retorting processes include different methods for imparting the heat of pyrolysis to the oil shale. For example, the heat may be imparted by heat-carrying gases which generally are combustible, although not necessarily so. it may be supplied in a sectioned retorting process such as is disclosed in our copending U.S. application Ser. No. 781,754, filed of even date herewith. in another process developed in Brazil, there is no preheating section and all of the heat is supplied by the circulating gas taken off the retorting bed. in another process, hot ceramic balls are charged into a retorting drum with the raw shale oil to supply the heat of pyrolysis. A further process has hot burned off spent shale mixed with a raw whale charge to provide the heat needed. There have also been attempts at in situ processes with combustion gases in the field. These various retorting processes are usually conducted at temperatures of from 500 to 1,500 F., generally 800 to l,000 F. The raw shale feeds are crushed oil shale particles, e.g. generally about 1/4 inch or 3/8 inch to l inch in size up to about 3 inches. if desired, feed sizes less than V4inch can be used.

in the processes described above, the composition of the atmosphere is usually not controlled but is composed of the products from the retort zone and/or extraneous gases which in appropriate cases includes any heat-carrying gas supplied as well as the products of combustion and retorting, it has, however, now been found in accordance with this invention that the yield from the retorting of carbonaceous material is markedly improved by controlling the composition of the atmosphere of the retorting zone. An atmosphere of natural gas or a gas of similar composition significantly increases the yield and natural gas containing up to 20 percent carbon dioxide can give even better results. 3

The invention will be described in detail hereinbelow with reference to the appended drawings in which:

FIG. 1 is a graph of oil yield versus retort atmosphere of natural gas with varying carbon dioxide content.

FIG. 2 is a graph of oil yield versus residence time in a retorting zone at different temperatures and atmospheric control conditions.

In accordance with this invention, it has been found that the composition of the atmosphere surrounding the oil shale particles at the time of pyrolysis has a definite effect on the oil yield obtained from the retorting pyrolysis. The atmosphere corresponding to combustion within the bed with air, or air partially denuded of oxygen, as frequently used in gas combustion retorting, gives the lowest yields. For example, oil shale was retorted in the laboratory in a 4-inch diameter batch fluidized bed at a temperature of9l5 F. A fluidizing gas was used containing about percent oxygen, as might be used in a typical conventional, gas combustion retort, and the oil yield was about 85 to 88 weight percent Fischer Assay oil. Natural gas in the same equipment and at the same temperature gave a higher yield of about 102 weight percent Fischer Assay oil. A mixture of 90 vol. percent natural gas and i0 vol. percent carbon dioxide gave the highest of all, around 107 wt. percent of Fischer Assay oil.

This unexpected discovery is applicable to all types of oil shale retorting processes. in our copending U.S. Pat application Ser. No. 781.754, there is described a sectioned retort process which is further enhanced by atmospheric control as herein disclosed. The instant invention is applicable to continuous or batch processes and requires only that the at- I mosphere be controlled for maximum yield. The invention is also applicable to in situ retorting processes. This control can be achieved, for example, by an online chromatograph which analyzes the off gas from the retorting apparatus and which controls the injection of the gases to be used through conventional control means. The injected atmosphere can be obtained by mixing natural gas or another light hydrocarbon gas with the gaseous product from the retort, which contains carbon dioxide, to obtain the desired concentration of carbon dioxide in the retort fluidizing gas. in some cases, the concentration of carbon dioxide in the gaseous product from the retort will be the concentration desired in the retort fluidizing gas. In such cases, natural gas or another light hydrocarbon gas would be used only to start the unit, and for occasional makeup necessitated by upsets or leaks.

The following examples further illustrate the invention.

EXAMPLE 1 A batch-type oil shale retorting process was undertaken utilizing natural gas atmosphere that contained various percentages of carbon dioxide. The retorting temperature, pressure and residence time were approximately constant. The results are given below in table 1 and depicted graphically in FIG. 1.

TABLE I Retort tem- Residue Oil yield Vol. percent CO2 (balance perature time ,(wt. percent natural gas) F. (min.) F.A.)

This data shows that the maximum oil yield is obtained at approximately 10 percent carbon dioxide, balance natural gas with yields greater than that obtainable with natural gas alone being obtained when using up to about 20 volume percent carbon dioxide diluent.

EXAMPLE 11 A retorting process and retorting environment were used wherein the bed composition was kept essentially constant throughout the run with a variety of residence times utilized, none of which were sufficient for complete retorting of all the feed. The details of the process are described in our copending patent application Ser. No. 78l,754. Regardless of the retorting temperature, retorting pressure and residence time employed for a specific series of runs, the effect of increasing yields by adding carbon dioxide to a natural gas fluidizing gas as the process retort fluidizing gas is exhibited. The data is given below in table 11 and depicted graphically in FIG. 2.

TABLE II Retort tem- Average Oil yield perature residence (wt. percent Fluidizing gas composition F.) time (min.) F.A.)

The data of the examples thus shows that the use of a natural gas atmosphere and natural gas containing up to about 20 volume percent carbon dioxide either in batch or continuous By withdrawing the maximum yield of oil, the residue of spent shale is combustible and may be burned elsewhere. The injection of the gas needed to control the atmosphere during retorting will also lower the dew point of the oil shale vapors as they leave the retort, and, thereby facilitate the removal of entrained dust by maintaining a gaseous or vaporous atmosphere for the first stages of dust recovery. It will also help prevent condensation of oil in transfer lines between the retort and the oil processing system.

We claim:

1. A process for the recovery of volatile material from carbonaceous material by retorting the carbonaceous material in a retort, the improvement which combines controlling the atmosphere surrounding the carbonaceous material during pyrolysis so that it consists essentially of a gas selected from the group consisting of natural gas, a gas from said retort similar to natural gas, a mixture of gaseous product from said retort with a light hydrocarbon gas, and a mixture of natural gas a gas from said retort similar to natural gas, or a mixture of gaseous product from said retortv with a light hydrocarbon gas with carbon dioxide.

2. The improvement of claim 1 wherein the carbonaceous material is oil shale and the volatile material contains oil.

3. The improved process of claim 2 wherein the atmosphere contains up to 20 volume percent carbon dioxide.

4. The improvement of claim 3 wherein the carbon dioxide content of the atmosphere is about heat-carrying 10 percent.

5. The improvement of claim 2 wherein the heat of retorting is supplied by a noncombustion supporting heat-carrying gas.

6. The improvement of claim 2 wherein the heat of retorting is supplied by hot ceramic balls.

7. The improvement of claim 2 wherein the heat of retorting is supplied by mixing hot spent shale with raw shale.

# i i i 32 13 UNITED swims mfrsm." ormcs CER'PIFItCATid OF CORF'lECiION Patent No. 3,6l7, L67 d November 2, 1971 Inventofls) Alan K. Revburn. Rex T. Ellington, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 2 "removing volatile material, such as combustible gasses, liquid" should read ---removing volatile material, such as combustible gases, liquid--- Column 1, line 22 "mixed with a raw whale charge to provide the heat needed." should be ---mixed with a raw shale charge to provide the heat needed.--

Column l, line 10 "content of the atmosphere is about heat-carrying 10 percent." should read --content of the atmosphere is about 10 percent.

Signed and sealed this 2nd day of May 1972.

(SEAL) Attest:

EDWARD' M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. The improvement of claim 1 wherein the carbonaceous material is oil shale and the volatile material contains oil.
 3. The improved process of claim 2 wherein the atmosphere contains up to 20 volume percent carbon dioxide.
 4. The improvement of claim 3 wherein the carbon dioxide content of the atmosphere is about heat-carrying 10 percent.
 5. The improvement of claim 2 wherein the heat of retorting is supplied by a noncombustion supporting heat-carrying gas.
 6. The improvement of claim 2 wherein the heat of retorting is supplied by hot ceramic balls.
 7. The improvement of claim 2 wherein the heat of retorting is supplied by mixing hot spent shale with raw shale. 